The present invention relates to X-ray imaging radiography and, more particularly, to a novel method and apparatus for high-pressure gas ion-flow electro-radiography utilizing direct charge readout of a charge image in a closed exposure chamber.
Conventional X-ray imaging techniques, typically using the screen-film system, are being replaced with electroradiography, whereby X-rays, differentially absorbed in an object under analysis, cause the deposition of an electrostatic charge image on an insulative sheet for subsequent development by electrophotographic techniques. The differentially-absorbed X-ray image may be converted into an electrostatic charge image, as is well-known in the art by use of high pressure gases, such as Xenon, Krypton and Freon 13B1, as the radiation-to-charge conversion material. Apparatus for providing radiographs using an ion-flow electron radiography technique, is described and claimed in pending U.S. patent application No. 942,548 filed Sept. 15, 1978, assigned to the assignee of the present invention and incorporated herein by reference. In the apparatus of the aforementioned application, the differentially absorbed X-radiation enters an exposure chamber through an upper electrode and is converted to electrical charge in a gaseous or liquid conversion material. The resulting charge is collected, under influence of an electrostatic field, upon the surface of an insulative layer, supported by a conductive mesh. The charge-image-bearing mesh structure is moved into an adjacent developing chamber, wherein ions are projected through the mesh structure towards an electrode spaced from the insulator layer portion of the mesh structure, for deposition of an ion image upon a dielectric sheet supported by the electrode. The mesh structure is moved back into the imaging chamber, which is subsequently filled with the conversion material, in preparation for a subsequent X-ray exposure. The dielectric film, having received the image-forming charge pattern, is removed from the developing chamber for subsequent development using electrophotographic techniques. The insertion and removal of the image-receiving dielectric film from the chambers containing high-pressure gas is difficult if loss of some quantity of the expensive conversion gas is to be prevented. Accordingly, a method and apparatus allowing the direct readout of the image-forming charge pattern, from a closed chamber containing a high pressure X-ray-to-electrostatic charge conversion gas, wherein the chamber is never opened and the expensive conversion gas is not lost, is highly desirable.